1. Field of the Invention
The present invention relates to the texturing of yarn by false twisting.
2. Description of the Prior Art
An end of thermoplastic yarn consisting of a few filaments, i.e., one, two, three or four, is not entirely satisfactory for being frictionally clutched by the friction disc or discs of a false twist device because while the individual filaments may be round in transverse section, the end of yarn is not round in transverse section. For example, as a two filament yarn is twisted, first one filament, then both and then the other are presented to the rim of the friction disc in repeating cycles for being clutched. Since part of the effectiveness of the friction disc for twisting the yarn is dependent upon whether the rim of the friction disc clutches only one or both filaments, it follows that the effectiveness of the friction disc for twisting the yarn fluctuates. As a consequence, the segment of yarn passing over the rim of the friction disc vibrates or oscillates, i.e., moves perceptively back and forth from side to side circumferentially of the friction disc. The movement may be observed with the naked eye as a shadowy area. This is one of the principal causes of the uneven texturing which results from false twisting effected by the friction disc or discs of a false twist device.
It is common knowledge that if a bow is drawn across a string which is drawn taut, the string is set to vibrating. In like manner, since the yarn passing over the rim of a friction disc in contact therewith for being twisted is tensioned, it is set to vibrating when the friction disc is actuated. The vibration is in the fundamental mode, i.e., the two points at which the yarn is restrained against vibration, respectively on opposite sides of the disc, are the only nodal points, and the center is the only antinode. For the fundalental mode of vibration the yarn segment forms one loop, which has a length equal to a half wave. The resulting vibration or oscillation, superimposed upon the movement noted hereinbefore, contributes materially to the uneven texturing which results from false twisting effected by the friction disc or discs of a false twist device.